How to stop water leaking through my tile grout joints?


I have 2x2 inch mosaic tile in a handicap shower I am having trouble with water seeping through the tile grout an leaking in the crawl space below. What would be the best way to seal the grout? Thank you for your answer


ANSWER - If water from your shower is leaking into a crawl space the problem is not the cementitious grout joints.  There has to be an underlying problem with the shower pan's waterproof membrane.  It likely was not installed correctly.

To waterproof a shower pan and shower walls, you have to have a waterproof membrane that meets ANSI A118.10 to be properly installed.  The plumbing code says that the waterproof shower pan liner has to extend up at least 3 inches above the height of the top surface of the dam/curb.  Along with having a moisture barrier sheeting behind the wall substrate so it weather laps over the shower pan liner.

Apparently your waterproof membrane is not working as it should or you wouldn't have a leak into the crawl space.   The proper way to fix this problem is to remove at least the shower pan and reinstall it correctly.

If you have a limited budget and want to take a risk, there is a possible fix that doesn't meet the standards.  You could remove the cementitious grout from the grout joints, remove the grout in the shower pan floor to wall horizontal transitions, and remove the grout in the inside corners of the wall tile.

The once the joints are open and clean, use an ASTM C920 silione sealant and fill all of those joints.   If your 2x2 inch tile is porcelain and you have these grout joints filled with sealant, in theory, if you do everything correctly, water should not be able to pass through.  You might have to do the same thing with all of the grout joints on the wall tile.

This method doesn't come with a guarantee and only proceed at your own risk.

8 thoughts on “How to stop water leaking through my tile grout joints?

  1. Dave Anderson says:

    It’s nice to know how my shower grout leak will be fixed, but I don’t know how to repair or replace it. I think I am going to call a grout repairman and have them come to fix it now that I know what the problem might be. I want this grout problem fixed effectively.

    • Donato Pompo says:

      It isn’t a grout problem. It is a waterproof problem. The grout problem is a symptom of the waterproof problem.

  2. Leslie says:

    I have a small backsplash in a bathroom to grout. If I put a thin layer of caulking on before I grout, will the grout still breath, dry out, and not mould if it gets wet? Or will the calking behind the grout mould?

    • Donato Pompo says:

      If you use a quality caulking/sealant per industry standards would be an ASTM C920 sealant such as a 100% silicone sealant it should keep water out. Grouting over the sealant with a cementitious grout wouldn’t be recommended as it may not perform well and it will limit the performance of the sealant. I would grout the entire grout joint with the silicone sealant.

      Use blue masking tape along the edges of the tile before applying the sealant. After applying the sealant pull of the masking tape right away otherwise it can be problematic.

  3. M Lynn Cooper says:

    I have a leak coming into my tile shower. My home is new and the plumber and the tile expert cannot explain what or why it is leaking. The leak is on a non-plumbing wall and only leaks after my shower has been in use. The leak is located on the floor next to a bench seat . Help!

    • Donato Pompo says:

      You know that the leak is caused by using the shower. The question is what is the source of the leak and where is it located. If you know that, then you can determine how to remediate it.

      The source of a leak is often not where the the water leak exits. It could be due to a plumbing pipe even if the leak is adjacent to a non-plumbing wall. You know that the leak only occurs when the water is on, so that means it isn’t a leaking pipe. If it is the plumbing it is occurring where the water is coming out at the values.

      Often we find that a shower bench has not be properly waterproofed or sloped. If that is the case then water can be entering though the tile grout joints and transitions joints and leaking into the bench and then out of the bench. The bench should have been fully waterproofed and sloped a 1/4″ per foot towards the drain. The only way to determine if it was constructed correctly is to forensically remove certain tiles to see how it was constructed.

  4. Thanh says:

    I have tub with a shower. It seems to be leaking down to the basement on far end away from the plumbing. I filled tub; it doesn’t leak. In the process of filling tub I used the faucet and didn’t notice leak. I let shower run without anyone inside and didn’t notice leak. I sprayed the shower wall close to shower head side and noticed a leak but it came down on another location in basement. Why the difference in leak location? More than one leak source? Could the leak run down the sliding glass door and down basement?

    • Donato Pompo says:

      That is the challenge with water leaks that where the leak shows up can be no where near where the water source is located.

      Generally speaking in a bathtub the areas most likely to allow water to leak out is at the tub transpositions. That can be from the tub to the walls or at the windows or at glass partitions. So you should clean those transitions and caulk them with an ASTM C920 sealant like a pure silicone or polyurethane. Try that and see if it works.

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